The chapter headings in this book are the sort of questions we have to answer repeatedly: When were you born? What is your mother's name? What is your father's occupation? A foundling can answer none of these questions. Kate Adie, adopted but not abandoned, eventually found some of the answers, although the place of birth on her passport is a lie. She doesn't "give a hoot", but there are, and always have been, countless thousands of others, abandoned as babies, in foundling hospitals, phone-boxes, cars or trash-cans, who will never know the answers to such questions and whose lives are far from successful.

The numbers of abandoned children in the world are quite shocking, as cited by Adie, who maintains the reasons for abandonment "have never strayed far from poverty, shame, inheritance and indifference". The harsh treatment of these children on such a grand scale is even more appalling, but this is not a dreary or polemical book. It is witty, gripping and deceptively lightly written. Adie's empathetic interviews reveal stories of success, resilience and determination to improve the lot of foundlings internationally. But the people who are fighting for this are up against formidable opponents: religion, society's disapproval, shame and general meanness. Who, after all, is going to pay for the upkeep of these foundlings? No government has ever been keen on stumping up for a decent life for the children of sin.

A foundling may sound romantic to some; Adie reminds us of Tom Jones, Romulus and Remus, Heathcliff, Moses and Oliver Twist. "The idea of redemption or rehabilitation runs through a good many stories", but in truth the great mass of foundlings were "disciplined in institutions, creatures of charity ... always bound up with the idea of service", including prostitution and slavery - "a notional fine for having appeared improperly".

Somehow, blame always fell on the child; even Oscar Wilde's Jack Worthing in his "handbag" was reprimanded for losing two parents, and the Christian church seems to have popularised this idea. Once it "began spreading its influence and refining laws about sexual behaviour [illegitimacy] became gradually unacceptable - a sin for both mother and child". Fathers get off lightly. They are "rarely mentioned in the context of responsibility". In the 1750s, mothers delivering their children in person to London's Foundling Hospital formed "a procession of women betrayed".

Adie's extensive travels and personal experience enrich her narrative and also provide a sweeping view of the world's dealings with foundlings. She has been to the specialised institutions, dating back to the 14th century, with their revolving wheels, or turntables, upon which the mother could anonymously place her baby and "with one turn" deliver it safely into the building. Unfortunately, "survival was not built into the system", and mortality rates were appalling. Even in the greatest of these institutions - the Innocenti in Florence - "90 per cent didn't make it through their first year". The reasons for this were hygiene, overcrowding and illness, but also "the almost complete absence of cuddling and affection, of regular, warm human contact".

Poverty frequently led women to abandon their children, but by the 17th century, thanks again to the teachings of the Catholic church, "shame and sin had been added in bucketfuls". Improvements have been horribly slow. In 19th-century New York's foundling hospital, the "same dreadful mortality rates were being replicated". Orphan trains ferried foundlings to the American West until the 1930s; the Irish Magdalen laundries, "a disgraceful hangover of medieval prejudice ... continued into the 1990s"; and while Russian orphanages may still be "grim, wretched and rigid", "50 children were found in rubbish bins" in Texas in 1999.

With her use of restrained but rather acid comments, Adie has effectively demolished the staggeringly batty notions that a child is to blame for its parents' actions or that bad blood will out. For these fantasy misdeeds, millions of children in many countries, for centuries, have been punished, often for the rest of their lives. They were not allowed to open their wings and fly, but were forced to knuckle down and be drudges. What an enormous waste of potential, but who cares? Because we have always needed cannon fodder and servants.

But even foundlings who survive to live a happier life may forever long to know the answers to Adie's list of questions. "One child wrote from her pleasant new home: 'I would give a hundred worlds like this if I could see my mother.'"